In the related art, a film forming method is known in which a thin film is formed by sequentially supplying at least two kinds of mutually-reacting reaction gases to a surface of a substrate and laminating a plurality of reaction product layers through the execution of this supply cycle. The film forming method includes a step of mounting a substrate on a rotary table installed inside a vacuum container and rotating the rotary table, a step of supplying a first reaction gas and a second reaction gas to a surface of a region (on which the substrate is mounted) of the rotary table from a first reaction gas supply means and a second reaction gas supply means which are installed in the vacuum container in a spaced-apart relationship along a rotational direction, and a step of supplying a separation gas from a separation gas supply means installed in a separation region defined between the first reaction gas supply means and the second reaction gas supply means in the rotational direction and diffusing the separation gas toward a narrow space defined between a ceiling surface of the vacuum container and the rotary table at the opposite sides of the separation gas supply means in the rotational direction.
In such a film forming method, the reaction gas and the separation gas diffusing toward the opposite sides of the separation region are exhausted from an exhaust port of a first exhaust path opened between a first processing region and the separation region adjoining the first processing region at the downstream side in the rotational direction when viewed from the rotation center of the rotary table and an exhaust port of a second exhaust path opened between a second processing region and a separation region adjoining the second processing region at the downstream side in the rotational direction when viewed from the rotation center of the rotary table. The film forming method includes a step of mutually independently exhausting the gases from the first processing region and the second processing region and a step of mutually independently exhausting the interior of the first exhaust path and the interior of the second exhaust path with a first vacuum exhaust means and a second vacuum exhaust means. The first reaction gas and the second reaction gas are independently exhausted from the first processing region and the second processing region. Since a clearance space existing under the rotary table is configured to have an extremely narrow size, the first reaction gas supplied to the first processing region and the second reaction gas supplied to the second processing region are mutually independently exhausted from a first exhaust port and a second exhaust port without passing through the underside of the rotary table.
However, as the process is diversified in recent years, it is often required that the process is performed in a state where a clearance is formed in the underside of a rotary table. Specifically, in a high-temperature process, when a wafer is loaded into a vacuum container and mounted on a rotary table, the wafer may be largely warped. A process cannot be started until the warp is settled. In order to rapidly start the process even a little bit, the rotary table is often configured to move up and down. When mounting a wafer, the rotary table is moved down to enlarge a space. If a warped portion is settled, the rotary table is moved up to perform the process.
In such a process, since the process is performed in a state in which the rotary table is moved up, a clearance is generated under the rotary table. The first reaction gas and the second reaction gas are mixed with each other in the clearance. This may make it impossible to independently exhaust the first reaction gas and the second reaction gas. The first reaction gas and the second reaction gas may react with each other to generate a reaction product. Therefore, if the first reaction gas and the second reaction gas react with each other in the vicinity of the first exhaust port or the second exhaust port, an unnecessary reaction product may be generated in the first exhaust port or the second exhaust port. Thus, the interior of the vacuum container may be contaminated.